The present invention relates to a ceramic heater and its manufacturing method, the ceramic heater being applicable to an oxygen concentration sensor with a heater, the sensor being used to detect an oxygen concentration in an exhaust gas exhausted from a vehicular internal combustion engine.
In general, in an automotive vehicular internal combustion engine on which a turbo charger is mounted, the engine is operated with an air/fuel mixture ratio (air excess rate) which tends to be rich so that a temperature of an exhaust gas from the engine reaches approximately 250.degree. C. However, since a zirconia tube which constitutes a detecting element of the oxygen concentration sensor is normally operated under a temperature around 350.degree. C., the oxygen sensor with the heater is used in the turbo charged internal combustion engine so that the zirconia tube is heated and used as the oxygen concentration sensor.
A Japanese Patent Application First Publication No. Heisei 6-235716 published on Aug. 23, 1994 exemplifies a previously proposed ceramic heater and its manufacturing method.
Although the above-described Japanese Patent Application First Publication describes a curved surface printing of a heating pattern on a ceramic heater main body, a specific form of the heat pattern which indicates a superior, constant heat performance and which indicates a high yield is not described in details, only indicating an axially extended pattern.
Therefore, there is an industrial demand in the manufacture of the ceramic heater that constant resistance value and heat generation quantity can be managed for each manufactured ceramic heater.